7 Sensation

Sensation Chapter 5 p193

Sensation Sensation is the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment Perception – The process of organizing and interpreting information, enabling us to recognize meaningful objects and events

Information Processing Bottom up Processing – analysis that begins with the senses and ends in the brain Top Down Processing – information processing guided by higher level mental processes, influenced by expectations and experience

Thresholds Psychophysics – study of how energy (stimuli) affects psychology. Absolute Threshold – The minimum stimulation needed to detect a particular stimulus at least 50% of the time. Single Detection Theory – Theory that there is no static absolute threshold but that it changes depending on a person’s experience, expectations, fatigue level, etc

Subliminal Messages Subliminal – stimuli below the absolute threshold. Studies show that subliminal stimuli may still have some affect on our thinking or dispositions. Subliminal stimuli still register in our subconscious and can affect general moods or prepare us to process some information faster but it cannot be used to give detailed “suggestions” that we are unaware of.

Difference Thresholds Difference thresholds – the minimum difference you can detect between any two stimuli at least 50% of the time. Weber’s law states that the difference threshold is determined by % difference change, not a constant amount.

Sensory Adaptation Sensory adaptation is the diminishing sensitivity of a stimulus as a consequence of constant stimulation. Transduction – the changing of stimulus energies into electrical impulses for our nervous system.

The Eye The Stimulus – LIGHT! Light is actually a part of something called electromagnetic radiation (energy). Electromagnetic energy is measured in waves, Some basic wave properties are wavelength and Amplitude

Wave Properties For light, the wavelength determines the color or hue. The amplitude determines the brightness or strength. For sound, the wavelength is the pitch and the amplitude is the volume.

The Eye

Acuity People who have trouble seeing usually have problems with Acuity. The cornea and the lens are supposed to focus light directly on the retina, if they don’t and the image is focused before the retina you are nearsighted, if the image is focused behind the retina you are farsighted. Glasses or contacts simply bend the light so it focuses in the right place.

The Retina The back of the eye is called the Retina this is where transduction occurs. There are many special cells that work together. Rods are light detection cells that detect low levels of light in black and white Cones are detection cells that are better at detecting detail and can detect color, most cones are located in the fovea, the center of the retina where most of the light reaches.

The Retina Bipolar cells send messages from cones and rods to Gaglion cells. Many times several rods are connected to a bipolar cell, whereas sometime a single cone with be connected to another. This means that rods help us see at night more, but cones can reveal more detail. Ganglion cells axon’s form the Optic Nerve and carry the sum of information of the 130 million rod and cone receptors to the brain.

Visual Processing Feature Detection – The brain processes visual information in pieces. There are parts of the visual cortex that respond to specific stimuli such as movement, a line drawn at a particular angle, color, curves, depth perception, etc. All of these features together form a picture for your mind.

Parallel Processing The brain processes millions of signals at the same time combining all the information to form a complete idea, thought or picture in your mind.

Color Vision The human eye can discriminate between over 7 million colors Young-Helmholtz trichromatic theory – State that the retina has three types of color receptors each specially sensitive to one of the three primary colors: red, green, or blue. Most color deficient people are not totally color blind, they lack red or green functioning cones so they have trouble distinguishing between red and green.

Color Vision Color processing occurs in two stages. First the retina reads red, green, or blue However as the signal is sent to the brain it goes through another process. The opponent process theory states that some neurons be excited when they detect red but inhibited with green, or the opposite. This also happens for blue and yellow, and black and white.

Color vision This means that you cannot detect both colors at once, so you will never see a greenish red – but instead you perceive yellow. Color Constancy – The other important factor regarding color vision is that your perception of color depends not only on the wavelengths detected in your retina but your brain’s processing of it in the context of other colors or environment – this is especially important for things like art, fashion, interior decoration etc.

The Ear

Transduction Transduction occurs in the Cochlea in the inner ear. The Cochlea is lined with up to 16000 little hair cells that stand in fluid. As the sound waves are conducted to the Cochlea the hairs move back and forth to the vibrations and their movement triggers electrical neural impulses.

How do we perceive Pitch? There are multiple theories on how we notice pitch. Place theory states that you determine pitch based on where on the cochlea’s membrane the hair cells are stimulated. Frequency theory states that the hair cells vibrate with the same frequency of the sound wave and your brain can tell pitch by the frequency of neural signals sent.

How do we perceive Pitch? Both theories do not completely explain how we hear pitch. Neurons can only fire upto 1000 times a second, yet we can hear at frequencies much higher than that. Place theory also does not explain how we hear low frequency sounds because neuron firing is not localized to one area when low frequency sounds are heard. Thus place theory is good for high pitch and frequency theory explains low pitch.

Locating sounds You brain can tell which direction sound is coming from by which hear hears the sound first, as well as the differences in volume from one ear to the next.

Hearing Loss Conduction Hearing Loss – hearing loss that occurs when the mechanical process of conducting soundwaves from the ear drum to the cochlea is disrupted (for example a punctured ear drum.) Sensorineural hearing loss – hearing loss due to the damage of the cochlea’s haircells. (cannot be repaired)

Touch The skin has four distinct senses Pressure Warmth Cold Pain

What is Pain? Pain is dependant on both the physical sensation of it, the region that it comes from and the Brain interpreting it. 7 out of 10 Amputees report feeling pain in their missing limbs – so pain is partially controlled by the mind. There are no particular pain receptor’s.

Gate Control Theory Gate control theory explains some aspects of pain. According to this theory pain messages travel to the spinal cord in smaller nerve fibers which are turned off if there are also signals coming from larger nerve fibers or can be turned off by messages coming from the brain. Thus if you stub your toe, you rub the area around it to stimulate the larger fibers and try and turn some of the pain messages off.

Psychology of Pain Seeing other people in pain often makes you more aware of your own pain. People feel more pain when they see others suffer. People remember the worst parts of pain, but not the length of time in pain. Pain control – Options include drugs (endorphin affecting opiates) surgery, acupuncture, electrical stimulation, massage, exercise, hypnosis, relaxation training, and thought distraction. Example: Lamaze techniques use, counterdistraction (massage), thought distraction, and relaxation techniques.

Taste Taste, like touch has four basic sensations Sour Bitter Sweet Salty

Taste Taste is a chemical sense Inside each bump on the top and sides of your tongue are 200 or more taste buds. These taste buds trap food chemicals in a pore that are then sensed by 50 to 100 taste cells that project hair-like receptors into the pore. Taste receptors grow back every two weeks or so, so if your burn them accidentally you won’t have permanent taste loss. However, as you grow older the number of taste buds decreases, so often adults like more flavorful food than children.

Taste, fast facts Taste is instinctual. You are born liking sweet flavors and disliking bitter flavors. There are taste receptors in the back and roof of the mouth as well, you don’t have to have a tongue to taste. Smell is also a chemical sense, the senses of taste and smell are linked.

Sensory Interaction The brain combines all data from the senses to create a total “picture” or “reality” that we perceive. If you smell something bad but taste something good, often the food experience will be ruined. Senses interact and your brain blends them together to create what you believe is actually happening.

Smell

Smell is one of the oldest senses. Smell takes place in the nasal cavity where many olfactory receptors react singularly to particular chemicals in the air. Some chemicals may trigger more than one receptor and get interpreted as a separate scent. Smell can be very distinguishing, many animals can distinguish individuals just by scent as well as some people who have heightened smell senses (such as a blind man). Smell is the only sense that has a direct nerve hard-line to the limbic system which deals with emotions and memory. This is why some smells can strongly evoke an emotional memory.

Kinesthesis

The body has millions of motion and position sensors that tell the brain where your body parts are and where they are moving. This is called Kinesthesis. A separate sense using the semicircular canals in the middle ear specifically monitor’s the head’s position and movement – vestibular sense. Without these senses physical activity would be impossible to coordinate.